I’ve looked into this, in order to transition from software engineering into a cybersecurity niche it requires a drastic pay cut. Sure if you’re the self-employment type you could try doing bug bounties, but the top 1% make like 35k a year on average, and everyone else makes peanuts or zero. That is still better than starting a startup, but you're also better off being a day trader where 10% of people make a better living with only 2 hours of trading a weekday and two hours of analysis and strategizing in the morning, maybe then you could find time to hack systems just for fun.
The other thing you could do is become some kind of consultant and make better money consulting companies and running pen tests for them, but if you can do that you could just as easily make more money building out and consulting on custom software solutions...
And if you don’t care about the money fine, but eventually someone that does care about money will come along and do it better than you anyway and eat your lunch.
Now, to leave this post on a positive note and not become a target for downvote gangs, I’ll propose this: the way to have more hackers at scale is to grow every software engineer to be a security conscious engineer by default, such that they are constantly looking for vulnerabilities throughout development and deployments to production. It works well because I’d say engineers spend maybe 4 hours a day actually working and the rest is thinking about problems, which can happen in parallel with hacking quite nicely.